lkml.org 
[lkml]   [2016]   [Jan]   [6]   [last100]   RSS Feed
Views: [wrap][no wrap]   [headers]  [forward] 
 
Messages in this thread
/
Date
SubjectRe: [PATCH v7 1/9] dax: fix NULL pointer dereference in __dax_dbg()
From
On Wed, Jan 6, 2016 at 10:00 AM, Ross Zwisler
<ross.zwisler@linux.intel.com> wrote:
> __dax_dbg() currently assumes that bh->b_bdev is non-NULL, passing it into
> bdevname() where is is dereferenced. This assumption isn't always true -
> when called for reads of holes, ext4_dax_mmap_get_block() returns a buffer
> head where bh->b_bdev is never set. I hit this BUG while testing the DAX
> PMD fault path.
>
> Instead, verify that we have a valid bh->b_bdev, else just say "unknown"
> for the block device.
>
> Signed-off-by: Ross Zwisler <ross.zwisler@linux.intel.com>
> Cc: Dan Williams <dan.j.williams@intel.com>
> ---
> fs/dax.c | 7 ++++++-
> 1 file changed, 6 insertions(+), 1 deletion(-)
>
> diff --git a/fs/dax.c b/fs/dax.c
> index 7af8797..03cc4a3 100644
> --- a/fs/dax.c
> +++ b/fs/dax.c
> @@ -563,7 +563,12 @@ static void __dax_dbg(struct buffer_head *bh, unsigned long address,
> {
> if (bh) {
> char bname[BDEVNAME_SIZE];
> - bdevname(bh->b_bdev, bname);
> +
> + if (bh->b_bdev)
> + bdevname(bh->b_bdev, bname);
> + else
> + snprintf(bname, BDEVNAME_SIZE, "unknown");
> +
> pr_debug("%s: %s addr: %lx dev %s state %lx start %lld "
> "length %zd fallback: %s\n", fn, current->comm,
> address, bname, bh->b_state, (u64)bh->b_blocknr,

I'm assuming there's no danger of a such a buffer_head ever being used
for the bdev parameter to dax_map_atomic()? Shouldn't we also/instead
go fix ext4 to not send partially filled buffer_heads?


\
 
 \ /
  Last update: 2016-01-06 21:01    [W:0.167 / U:0.332 seconds]
©2003-2020 Jasper Spaans|hosted at Digital Ocean and TransIP|Read the blog|Advertise on this site